X-ray fluorescence analysis using ultrasonic levitation technique

A thin film is used as the sample holder for analyzing solutions and solid samples using x-ray fluorescence (XRF). The incident x-rays are scattered on the sample and thin film, and the scattered x-rays serve as background signals in the XRF spectra. To reduce the intensity of the background signal, an ultrasonic levitation method was developed herein for XRF measurements. The ultrasonic levitation device is equipped with a transducer (horn) and reflector, and a small-size sample is levitated around a node of a generated standing wave; thus, a sample holder is not necessary. Fe solution (2 mu L) was analyzed to evaluate the developed instrument. The results obtained using levitation times of 0 and 60 min were compared. The solvent droplet almost evaporated during ultrasonic levitation; therefore, the absorption effects of XRFs and incident x-rays and the scattering effect of incident x-rays were reduced. At a levitation time of 60 min, the net intensity of the Fe K alpha peak was increased, and the background intensity decreased. The relationship between the levitation time and the net or background intensities of the Fe K alpha peak was defined; thus, condensation of the sample droplet was successfully observed. Quantitative analysis was performed using an internal standard method. The relative intensity (ratio of the net intensities of the target and internal standard elements) was proportional to the concentration ratio. Therefore, this method is useful for measuring trace elements at low background intensity and elucidating the process of condensation of a sample droplet.